This application is based on and claims the benefit of German Patent Application No. 198 01 875.4 filed Jan. 20, 1998, which is incorporated by reference herein
The invention describes a method for setting up a connection between a sending and a selected network element of a digital telecommunications network in accordance with the preamble of claim 1 as well as a network element in accordance with claim 16.
The article xe2x80x9cDistributed restoration in telecommunications networksxe2x80x9d by D. Johnson et al. (BT Technol. J. Vol. 12 No. 2, April 1994, pp 67-76) describes a method for the distributed restoration of connections in a telecommunications network that works based on the recommendations for SDH (synchronous digital hierarchy). The article describes how a connection between a sending and a selected network node is set up without the interference of a central management system. To this end a so-called xe2x80x9cflood searchxe2x80x9d is carried out in order to automatically identify alternative paths in a network after a connection or a network node fails. Each network node has a unique identification number (NID). If a physical connection between two network nodes fails, the network node with the lower NID becomes the sending network node and the other one the selected node. The sending network node now transmits the NID of the selected network node into a signature target field via all its back-up line systems, i.e. it signals the NID of the selected network node to its adjacent network node as the target signature. The adjacent network nodes continue to relay the target signature. If such a target signature reaches the selected network node, this means that there is a back-up path for restoring the failed connection. Now the selected network node sends a confirmation via the back-up path that was identified in this manner. Due to this confirmation, a physical connection is switched in all transit network nodes on the back-up path.
The article also mentions that in addition to using this distributed method for finding a path for restoring failed connections, it can also be used for other applications such as for switching a connection following a user request, for monitoring the network and for preventing overloads. In doing so, it also is possible to calculate a weight factor that takes the load of network nodes and connections into consideration in order to determine call metering.
The customary method is disadvantageous in that the free transmission capacity in the network is not used optimally since the signaling process is only possible between adjacent network nodes, i.e. only transmission capacity on the physical level between adjacent network elements is available as a back-up system for setting up a new connection. Another disadvantage is the fact that the path that is found must be retraced through a confirmation since it is not known per se even after the selected network node has received the target signature. Another disadvantage may be the fact that time may pass between the identification of possible paths and the switching of the connection. This means that a path that was identified in the meantime is assigned again by the time the selected network element sends back the confirmation and that consequently the connection cannot be set up. In addition, the customary method does not support protected connections and point-to-multipoint connections.
One object of the invention is to provide a method for setting up a connection in a synchronous digital telecommunications network that uses the free transmission capacity of the network better. Another object of the invention is to provide a network element that is suitable for carrying out the method.
The present invention provides a method and a network element for setting up a connection between a sending network element and a selected network element of a digital synchronous telecommunications network without the help of a central management system. The telecommunications network is logically structured based on a hierarchy with at least two multiplex layers based on a protocol that is used in the telecommunications network with each network element being able to access at least a part of the multiplex layers. Using a broadcast that is being sent by the sending network element to all other network elements, possible paths with free transmission capacity are identified between the sending and the selected network element. To this end, first the most suitable multiplex layer for setting up the connection is selected. The broadcast is relayed via existing connections of the suitable multiplex layers, which the respective relaying network element can access, and the connection is set up via one of the identified paths.
The invention is advantageous in that compared to the customary, central connection set-up, connections are established automatically and quickly. This allows for better customer service. The invention also restores failed connections faster. Another advantage is the fact that it is possible to react quickly to the changing load of the network, for example through ATM traffic.
Another advantage is the fact that the network load is reduced with the help of control data, so-called overhead.
Another advantage is the fact that the invention allows for a connection set-up based on the auto-dial of a user (customer), for example, by requesting the connection via the Internet or the World Wide Web (WWW). In addition, the method in accordance with the invention allows for a simpler connection set-up between two or several different network drivers or between different subnetworks.
Another advantage of the present invention is that it ensures that a path that is identified as suitable for setting up a connection is in fact available and is not used for a different purpose in the meantime.
By calculating a cost parameter as described in sub-claim 11, it is advantageously ensured that the most inexpensive or the most suitable path based on load can be used for setting up the connection.